Note: To access hidden files, navigate to /Users/<username> and the click the "Go" top menu drop-down and select "Go to folder..." Type ".sqldeveloper" (without quotes) and then follow the path from there. Directories that start with "." are hidden by default.

Once the above is saved, just try connecting from the main Connections Tree by right-click the connection and choose "Connect"

Note: To see what Java version you are running in OSX you can issue this at the cmd line: